The present invention relates generally to a seal for a universal joint cross trunnion, and in particular to a seal for a universal joint cross trunnion accommodated in a bearing bush for a universal joint shaft, the seal having an outer and an inner, ring-shaped, sealing body which are insertable into the bearing bush and operatively connected, and which permit mutual adjustment.
A sealing arrangement (German Patent No. DE 44 08 831 A1) for a bearing of a trunnion in a bearing bush for antifrictionally supported universal joints is known, the sealing arrangement being composed of a reinforced rotary shaft seal which is nonrotatably inserted into a bore of the bearing bush and engages on the trunnion via a sealing lip. Moreover, the sealing arrangement has a further reinforced sealing ring which is arranged in the region of an open end of the bearing bush in a manner that it nonrotatably engages on a shoulder of the trunnion and which is provided with a sealing lip directed toward the bearing bush. As a further component part, the sealing arrangement features a sealing cap which is retained on an outside wall of the bearing bush in a positive-locking manner and which forms a labyrinth gap with a reinforcement of the sealing ring. In this context, the prestress of the sealing lips, provided that they engage on a purely cylindrical step, is influencable only by the diameter tolerances of the respective component parts of the universal joint cross assembly, and can consequently be met. However, since, for manufacturing reasons, the transitions at the individual step changes are rounded, the cylindrical sealing surfaces are shortened in the axial direction, and the possibility of arranging a plurality of such sealing lips one after the other for improving the sealing effect in this manner is limited to the greatest possible extent.
Sealing systems in which the main sealing takes place on a conical transition between the cylindrical rolling body surface of the universal joint cross trunnion and the central universal joint cross body are known from German Patents Nos. DE 41 31 694 A1 and DE 196 54 234 A1. In this context, the required prestress can be met only with difficulty because of a possible addition or subtraction of manufacture-related length and diameter tolerances of the respective component parts of the universal joint cross assembly. Therefore, sealing systems of this kind possess an additional seal which is arranged before the main seal and which, on one hand, protects the main seal from direct contact with foreign matter and, on the other hand, is intended to increase the sealing effect. As a rule, these additional seals are stationarily arranged at the transition between the cylindrical rolling body surface of the universal joint cross trunnion and the central universal joint cross body. Their sealing lips are arranged in such a manner that the sealing takes place on the bearing bush of the main seal or a combination of bearing bush and main seal.
Another problem in sealing a universal joint cross assembly is the contour of the universal joint since, for manufacturing reasons, the transition between the cylindrical rolling body contact surface of the universal joint cross trunnion and the central universal joint cross body is conically rounded or designed in a step-shaped manner, including a cone or radius, or a step change, respectively. This transition between the universal joint cross trunnion and the central universal joint cross body serves as the sealing surface of the main seal, one or a plurality of sealing lips of the sealing system which, as a rule, is stationarily joined to the universal joint cross bush, engaging on the sealing surface with a specific prestress. This prestress must be guaranteed for functional reasons, since too low a prestress permits foreign matter to ingress into the bearing and excessive prestress gives rise to increased wear by abrasion, thus resulting in a premature bearing failure in both cases.
An object of the present invention is to configure and arrange the seal for a universal joint cross trunnion accommodated in a bearing bush in such a manner that a substantially long-lasting seal and, consequently, an improvement of the service life are achieved.
The present invention provides a seal for a universal joint cross trunnion (1) accommodated in a bearing bush (2) for a universal joint shaft, the seal having an outer and an inner, ring-shaped, sealing body (4, 5) which are insertable into the bearing bush (2) and operatively connected, and which permit mutual adjustment, wherein the two sealing bodies (4,5) feature meshing sealing elements (9) having a positive-locking design, at least the one sealing body (5) having an enveloping part (7) which overlaps the other sealing body (4) and/or the bearing bush (2) at least partially.
According to the present invention, the two sealing bodies feature meshing sealing elements having a positive-locking design, at least the one sealing body having an enveloping part which overlaps the other sealing body and/or the bearing bush at least partially. For this, it is advantageous for the two mutually opposing sealing bodies to have intermeshing sealing lamellae having a labyrinth-like design.
By the expedient design and arrangement of the two sealing bodies including the meshing, positive locking sealing elements and the appertaining enveloping part, a simple but very effective sealing device is provided in an inexpensive manner which ensures a long-lasting seal and, consequently, a substantial improvement of the service life.
According to a further development, an additional possibility lies in that the sealing bodies have one or a plurality of supporting elements, at least one supporting element resting on the universal joint cross trunnion in the region of a cone transition. In this manner, it is achieved that the sealing no longer takes place directly on the universal joint cross trunnion but via the intermeshing lamellar or labyrinth-shaped sealing elements which are in mesh or in operative connection with each other. In this context, it is advantageously possible for the outer sealing body to be joined to the bearing bush and for the inner sealing body to be joined to the universal joint cross via a force fit so that ingress of foreign matter or lubricant loss at the joining locations are prevented. To manufacture this sealing system which is composed of the outer sealing body and of the inner sealing body which both have a ring-shaped design, the outer sealing body can be manufactured in a cutting or non-cutting manner and subsequently be inserted into an injection mold on which, additionally, the contour of the inner sealing body is left open. In this manner, the inner sealing body can be injected so that is slightly shrinks while cooling down. Because of this, a labyrinth gap forms between the two sealing bodies which guarantees that inner and outer rings can be rotated relative to each other without producing large frictional losses. Prior to injecting the inner sealing body, a release agent is applied to prevent the two sealing bodies from sticking together. In this context, it is advantageous for the mutually opposing surfaces to have no irregularities, which likewise makes it possible to reduce frictional losses.
Moreover, it is advantageous for the two supporting elements to be arranged at a distance from each other, and for the second supporting element to rest on an inclined cone surface which is contiguous to the cone transition. By advantageously using the two supporting elements which are arranged at a distance from each other, these supporting elements can easily be mounted on the surface of the universal joint cross trunnion in the transition region between the cylindrical part of the universal joint cross trunnion and the cone transition, thus making it possible to obtain a perfect seal, in particular if these supporting elements are pressed against the surface of the universal joint cross trunnion with prestress.
It is also expedient that a chamber or recess directed toward the surface of the universal joint cross trunnion is formed between the two supporting elements. Because of the varying numbers of sealing lamellae or of the supporting elements which act as sealing lamellae, it is possible for the main seal to be adapted to different contours and conditions at the universal joint shaft or at the universal joint cross trunnion. Furthermore, it is possible to increase or reduce the height of the supporting elements or of the lamellar sealing elements without difficulty so that the cross-sectional height of the main sealing region can likewise be increased or reduced. Because of the reduction of the total mass of the sealing elements, structural space is gained, thus allowing the sealing elements to be placed on a step of a universal joint cross trunnion having a step-shaped design without difficulty, as a result of which the structural space available for the rolling element bearing arrangement can be enlarged.
In a preferred embodiment according to the present invention, provision is made for the enveloping part arranged on the inner sealing body to have an annular space which runs coaxially to a center axis and serves for receiving a ring-shaped extension arranged on the bearing bush.
According to the present invention, a ring-shaped extension arranged at the outer sealing body has a recess which is rectangular in cross-section and into which the outer part of the enveloping part is insertable.
Faces of the extension and of the recess running approximately parallel relative to a transverse plane may form in each case a ring gap with faces of the enveloping part of the annular space and of the annular space. Via the advantageous material selection and dimensioning, which both influence the individual force fits, it is possible to control the size of the labyrinth gap and thus attain the advantage that the main sealing effect is influenced only by the diameter tolerances. During assembly, both the outer and the inner sealing bodies are pressed onto their respective component parts and deformed within the elastic range. In the process, the labyrinth gap of the sealing system can be reduced again. By advantageously selecting these influence variables, it is possible for the friction between the inner and the outer sealing bodies to be minimized, thus resulting in a substantially wear-free seal.
The enveloping part and the two supporting parts may form the one-part sealing body which is composed of an elastomeric material and is pressed at least onto the universal joint cross trunnion and/or onto a cone part.
In addition, it is expedient for at least one supporting element to be designed as a sealing lip which rests on the cone part with prestress, and for the intermeshing sealing lamellae to extend approximately in the direction of or parallel to a transverse plane.
To limit the complexity of the sealing system according to the present invention, it is beneficial that the bearing bush features a bottom having an inner face, and that rolling elements are provided between this face and the inner faces of the sealing bodies for accommodating the universal joint cross trunnion, and that the ring-shaped extension of the bearing bush is inserted into the annular space of the inner sealing body.
An additional seal is obtained by a sealing lip premolded on the inner ring of the sealing body in conjunction with the universal joint cross cone. Due to the press fit of the inner sealing body on the universal joint cross trunnion, foreign bodies cannot ingress into the interior of the bearing bush. By the overlapping or enveloping part which encircles the other sealing body and/or the bearing bush at least partially, an additional seal is formed which advantageously protects, on one hand, the main seal having a labyrinth-shaped design and, on the other hand, the force fit between outer ring and bearing bush against foreign matter. The recess between the two supporting or sealing elements permits optimum control of the contact pressure in this region. Moreover, it is possible to insert a ring composed of elastomers into this recess and to achieve an additional sealing effect in this manner.